Automobile manufacturers are continually looking for ways to improve the fuel efficiency of automobiles. One way to accomplish this involves reducing the weight of the components used to construct automobiles. A commonly used method for reducing the weight of automotive weatherstrip formulations involves the use of foaming agents. The addition of foaming agents produces porosity in the cross section of the weatherstrip, thus providing a potentially dramatic savings in weight.
Automotive weatherstrip formulations can be composed of thermoplastic elastomers such as thermoplastic vulcanizates (TPV) or styrene-ethylene/butylene-styrene copolymer (SEBS) to achieve desired performance. Thermoset elastomers such as ethylene propylene diene monomer (EPDM) rubber can also be used for this type of application. Dense TPV and SEBS materials typically have a density in the range of 0.9 g/cc to 1.1 g/cc and are frequently blown using foaming agents to around 0.75 g/cc to 0.80 g/cc for microdense applications. Dense EPDM rubber formulations tend to have higher densities in the range of 1.1 g/cc to 1.3 g/cc and are blown using foaming agents to 0.85 g/cc-1.1 g/cc for microdense applications. Both approaches can be used to manufacture body-mounted weatherstrips for automobiles, but are relatively high in cost and result in seals with relatively high densities that do not offer significant vehicular weight savings.
Further, EPDM-based seals are likewise costly from a process stand point. The EPDM constituent ingredients are typically mixed together in a one- or two-step process prior to shipping to an extrusion facility. At the extrusion facility, the ingredients and rubber compound(s) are extruded together to form a final material, which is subsequently formed into automotive glass contacting weatherstrips. Hence, the extrusion process used to manufacture weatherstrips can include many stages, depending on the type of EPDM or other types of resins, and may additionally require long lengths of curing ovens. For example, extrusion lines of up to 80 yards in length that are powered by natural gas and/or electricity may be required. Much of the natural gas and/or electricity energy sources are used to fuel hot air ovens, microwaves, infrared ovens, or other types of equipment used to vulcanize the EPDM rubber compounds. The vulcanization process also produces fumes that must be vented and monitored to comply with environmental requirements. Overall, the processes used to fabricate these traditional EPDM-based seals can be very time consuming, costly, and environmentally unfriendly.
Mindful of the drawbacks associated with current TPV-, SEBS- and EPDM-based sealing technologies, the automotive industry has a need for the development of new compositions and methods for manufacturing weatherstrips, particularly foamed seals and sealing elements, that are simpler, lighter in weight, lower in cost, have superior long-term load loss (LLS) (i.e., ability to seal the glass and window for a long term), and are more environmentally friendly.